1. Field of the Invention
The present invention relates to a golf ball, and more particularly, to a solid golf ball with improved durability and flight performance, and a method of manufacturing the same.
2. Description of the Background Art
For a golf ball, hit feeling and flight performance thereof has conventionally been improved by setting the hardness of a core body, namely, the interior of a solid core, within a proper range. In order to provide favorable, in other words, soft hit feeling, a technique to particularly reduce the hardness of the solid core's center portion to increase a difference between the solid core's center hardness and surface hardness is most effectively used. It has been found that providing a large hardness difference in the solid core increases the amount of deformation upon hitting and thus a struck-out speed is increased with a decreased spin rate, resulting in improved flight performance.
In U.S. Publication No. US 2003/0073784 A1, for example, as a technique to reduce the solid core's center hardness without reducing the solid core's surface hardness so as to improve hit feeling without impairing durability and flight performance, a technique to add 0.01–0.5 parts by weight of sulfur and 0.05–5 parts by weight of an organic sulfur compound with respect to 100 parts by weight of a rubber component in a rubber composition of the solid core is proposed.
The technique in U.S. Publication No. US 2003/0073784 A1 aims to reduce the solid core's center hardness by a highly flexible crosslinking structure formed by the sulfur to ensure flight performance.
With the technique, it is possible to provide a large difference between the solid core's center hardness and surface hardness. However, the crosslinking temperature must be controlled precisely to set a crosslink density within a desired range, which sometimes makes it difficult to produce a desired rubber composition.